Recombinant DNA technology has recently become a powerful technology for manipulating foreign genes in transgenic fish, and enables functional analysis of gene expression in specific organs, tissues, and cells. Moreover, control of target gene (transgene) expression is required to establish transgenic fish for used in molecular and immune-related studies, or to generate transgenic fluorescent ornamental fish (Hsieh, J C et al., Tilapia hepcidin (TH)2-3 as a transgene in transgenic fish enhances resistance to Vibrio vulnificus infection and causes variations in immune-related genes after infection by different bacterial species. Fish Shellfish Immunol 29:430-439, 2010). The choice of promoter is an important consideration for control of transgene expression.
Myosin is a complex multimeric protein that plays important roles in contractile processes in eukaryotes. Myosin comprises myosin heavy and light chains, which have multiple isoforms with different spatiotemporal expression patterns (Parker et al., Characterization of the myosin lightchain-2 gene of Drosophila melanogaster. Mol Cell Biol 5:3058-3068, 1985). Some well-studied promoters are reported, including myosin light chain (Mlc2; phosphorylatable) gene family. In mice, the Mlc2 family includes three genes, expressed in fast skeletal muscle, cardiac and slow skeletal muscle, and smooth muscle and non-muscle cells, respectively (Shani, M, Tissue-specific expression of rat myosin light-chain 2 gene in transgenic mice. Nature 314:283-286, 1985; Lee, K J et al., Myosin light chain-2 luciferase transgenic mice reveal distinct regulatory programs for cardiac and skeletal muscle-specific expression of a single contractile protein gene. J Biol Chem 267:15875-15885, 1992). These Mlc2 isoforms may be a suitable model for investigating muscle-specific gene expression during different developmental stages. The zebrafish Mylz2 promoter has traditionally been used to ensure the integrity and expression of foreign genes in transgenic fish (Pan, C Y et al., Transgenic expression of tilapia hepcidin 1-5 and shrimp chelonianin in zebrafish and their resistance to bacterial pathogens. Fish Shellfish Immunol 31:275-285, 2011); it has been used to drive expression of fluorescent proteins in the muscle tissue of zebrafish (Ju, B et al., Recapitulation of fast skeletal muscle development in zebrafish by transgenic expression of GFP under the mylz2 promoter. Dev Dyn 227:14-26, 2003; Zeng, Z et al., Faithful expression of living color reporter genes in transgenic medaka under two tissue-specific zebrafish promoters. Dev Dyn 234:387-392, 2005). However, the zebrafish Mylz2 promoter is not suitable for driving expression of transgenic fluorescent protein in other fish species, including the convict cichlid (Archocentrus nigrofasciatus), as it results in only weak fluorescence in muscle, and the promoter is weaker than promoters of bream species. One way to resolve these problems would be to use skeletal muscle myosin isoforms from a different fish species; certain isoforms have been isolated and characterized, and are available (Rowlerson, A et al., Comparative study of myosins present in the lateral muscle of some fish: species variations in myosin isoforms and their distribution in red, pink and white muscle. J Muscle Res Cell Motil 6:601-640, 1985). It is desired to develop or construct a new promoter for driving expression of transgenic fluorescent fishes.